For example, to solve the problem that an exposed lead tends to pick up noise in testing a high frequency/high speed device such as a semiconductor wafer, IC, or module, a structure where electrode terminals 21 to 23 of a DUT 20 are connected to a test jig which contains an RF (this term means high frequency and high speed) signal probe 3, power supply probe 4, and ground probe 5 provided in a metal block 1, each of probes having a spring and a movable pin is disclosed in JP-A No. 99889/2001, as shown in FIG. 12(a). In such a test jig, RF signals are transmitted through a coaxial cable 7 to the RF signal probe 3, the spring is compressed to prevent a space from being formed between the DUT 20 and a thin presser board 8 on the metal block 1, and reliable contact between the RF signal probe 3 and an electrode terminal of the DUT 20 is achieved by means of the spring, thereby picking up as less noise as possible. In FIG. 12(a), 6 denotes a wiring board such as a printed circuit board in which a power supply circuit of the input side is formed.
In even such a structure, however, the probe in the metal block 1 tends to pick up noise in the high frequency/high speed device. In the above described JP-A No. 99889/2001, the RF signal probe 3 is coaxially structured, and thereby has no room for picking up noise. On the other hand, when the power supply terminal 23 picks up high frequency/high speed noise, it causes power supply voltage to change, an amplifier to oscillate, so it causes inaccurate measurement. To solve this problem, a low-pass filter 61 shown in FIG. 12(b), comprised of an LC circuit having coils L and capacitors C is formed on the wiring board (printed circuit board) 6, or a chip capacitor (bypass capacitor) is connected between the input side of the power supply probe 4 and a ground of wiring board 6, removing high frequency/high speed noise entered in the power supply circuit.
On the other hand, not only RF signals, but also various medium and low frequency signals in the range of DC level to 100 MHz are input for testing. A precise test cannot be achieved when RF noise is input to the signal terminals for medium or low frequency signals. Even if medium/low frequency input signal probes are coaxially structured, RF noise entered in the DUT side or test apparatus is input to the terminals of the DUT directly. Thus, a precise test cannot be achieved.
As described above, in order for the test jig not to be influenced by noise which the wiring connected to the DUT picks up, the portion for contact with a DUT is so structured that a contact probe having a movable pin which moves inward and outward by means of a spring is built in the metal block. In such a structure, no space between the DUT and the metal block is formed. The test jig thus hardly picks up noise. Additionally, as described above, the RF signal probe is coaxially structured in the metal block. On the other hand, with recent development of a high frequency/high speed device, its circuit has been high integrated and small packaged remarkably. Consequently, the number of the terminals (electrodes) is increased, and pitches between the terminals are shortened, so that noise tends to be superimposed not only onto a probe not built in the metal block, but also onto the power supply probe in the metal block. There is thus a problem that precise measurement without influence of noise cannot be completely achieved in the structure where the low-pass filter or chip capacitor are formed on the input side of the power supply probe.
Additionally, the present inventors found that an unexpected condition, such as an operation error and forced reset, tends to occur in testing the recent advanced high frequency/high speed device during the transition that the output becomes from low to high or high to low according to change of input signals. The reason for such a condition was found that the transition of the output voltage change becomes short and thereby the power supply current changes instantaneously to cause a voltage drop of the power supply terminal. In other words, when the source current increases stepwise, the power supply probe 4, which has a length of about 4 mm and is structured as shown in FIG. 12(a), has an inductance of about 2 nH (nano-henry) because of its narrowness. An equivalent circuit is shown in FIG. 11(a), when C2 is assumed 0.5 pF (pico-farad) as a floating capacitance around the probe (in FIG. 11(a), C2 shows the floating capacitance in the equivalent circuit, while a capacitor is not actually provided). As a result, when a current I1 changes from A1=10 mA to A2=50 mA stepwise (perfect condition, zero rise time), the voltage drops from 3 V to about 1.7 V, as shown in FIG. 11(c), causing an obstacle in the test data.
An object of the present invention is to solve such problems, in other words, to provide a capacity loaded probe which, for testing a high frequency/high speed device, almost influence of a voltage drop at the power supply terminal due to the presence of inductance, even if a pitch of power supply terminals is shortened and power supply probe is narrowed, because the device is highly integrated and small packaged.
Another object of the present invention is to provide a capacity loaded probe for achieving a noise-free precise test of a high-integrated high frequency/high speed device by reducing noise according to signals which is input to the terminals, and to provide a test jig for a test apparatus using the capacity loaded probe for testing a high frequency/high speed device or the like.